1. Field of the Invention
The present invention relates to a directional valve suitable for use in respiratory devices, the directional valve being of the type having a valve body and a valve seat with the contact surface with the valve body being substantially horizontal.
2. Description of the Prior Art
Directional valves are used in respiratory devices, anaesthetic machines in particular, to channel the direction of gas flow. One directional valve is generally installed in the anaesthetic machine""s inspiratory line and one directional valve in its expiratory line. Ideally, the directional valves should not affect expiratory resistance and inspiratory resistance for the patient nor interfere with measurements of flow in the anaesthetic machine. A conventional way to meet these conditions has been to devise directional valves with the lowest possible opening pressure. Such valves therefore generally are devised as disk valves, i.e. the directional valve has a disk-shaped valve body that rests loosely on a valve seat.
This type of directional valve has disadvantages. One disadvantage arises because moist gas is present in the anaesthetic machine. The valve body sometimes becomes wet, leading to surface tension that increases the opening pressure.
Other disadvantages are due to the shape of the valve body. If it is devised as a soft, lightweight disk, retrograde leakage could occur. Moreover, the valve body could be deformed enough by high back pressures to be pushed down into the valve opening. This would naturally be a serious problem, since the directional valve would then stop working. Retrograde leakage can be reduced by the use of a heavier directional valve, but this would naturally increase the valve""s opening pressure, and the valve body might then start wobbling. Stiff valve bodies (usually ceramic disks) could start to leak because of the deposition of calcium particles etc. on the valve seat.
An object of the present invention is to provide a directional valve that solves the aforementioned problems.
The above object is achieved in accordance with the principles of the present invention in a directional valve for a respiratory device, having a valve body and a valve seat, the contact surface of the valve seat with the valve body being substantially horizontal and the valve body containing ferromagnetic material, and the directional valve further having at least one coil which is magnetically couplable to the valve body, a source of current connected to the coil, and a control unit which regulates the current source to control the current through the coil so that the coil is magnetically coupled to the valve body in one or both of a closing direction and an opening direction.
When the valve body contains a ferromagnetic material and two coils are arranged with one coil on top of the valve body and one coil underneath the valve body, the valve body can be made to press against the valve seat or alternately lift off the valve seat by regulating the current flowing through the respective coils.
The directional valve can be operated as a servo system in an embodiment wherein the valve body contains a permanently magnetized material and a coil encircles the valve body and valve opening (to achieve the strongest possible magnetic coupling between the coil and the valve body). When the directional valve is to be in the closed position, a current is applied across the coil, generating a magnetic field that presses the valve body harder against the valve seat. This would accordingly reduce the risk of leakage.
When the directional valve is to be in the open position, the current is reversed, causing the electromagnetic field to lift the valve body. A minimal opening pressure is then achieved.
In the event of any loss of current, the directional valve would operate in the same way as a conventional directional valve. Directional valve operation is not interrupted. This is an important safety feature when the valve is used in anaesthetic machines and other respiratory devices.
Current through the coil is regulated from a source of current that is regulated, in turn, by a control unit. In principle, the control unit could regulate the source of current in such a way that directional valve operation parallels the respiratory device""s inspiratory and expiratory phases. The directional valve in the inspiratory line would then be open during inspiration and closed during expiration (and the reverse for the directional valve in the expiratory line). This kind of simplified regulation is only possible in certain limited conditions, e.g. no bias flow is used and the patient is not breathing spontaneously.
More refined regulation, tailored to different phases of respiration, e.g. during anaesthesia, is possible. The control unit therefore can control the source of current by sensing the valve body""s position. This can be achieved by inductive sensing of the coil. Alternatively, the EMF generated by the valve body""s movements can be sensed and employed for controlling the source of current. Any deformation of the valve body can even be sensed from changes in inductance.
Other parameters can also be used for regulation, for example, the pressure gradient between the inlet and outlet sides of the directional valve and flow through the directional valve. These parameters can be obtained either by providing the directional valve with a pressure gauge or a flow meter or by utilizing measurement signals from existing pressure gauges or flow meters in the respiratory device.